Non-hardenable aluminium alloy as a semi-finished product for structures

ABSTRACT

The present invention relates to the chemical composition of alloys, in particular naturally hard semifinished-material alloys, which are intended to be used in this form as material for semifinished materials.  
     Proposed is a naturally hard aluminum alloy for semifinished materials which, in addition to magnesium, titanium, beryllium, zirconium, scandium, and cerium, is also made of manganese, copper, zinc, and an element group containing iron and silicon, the ratio of iron to silicon being in the range of 1 to 5.

[0001] The present invention relates to the composition of alloys, in particular naturally hard semifinished-material alloys, which are intended to be used in this form as material for structures.

[0002] Naturally hard aluminum alloys are used in metallurgy as semifinished materials for structures (see GOST standard 4784-74), but primarily in the form of AMg6 alloy, which contains the following (in % by weight): magnesium 5.8-6.8 manganese 0.5-0.8 titanium 0.02-0.1  beryllium 0.0002-0.005  aluminum balance

[0003] However, such an alloy does not have adequate physical properties, in particular a low 0.2% yield strength in the case of cold-formed and hot-formed semifinished materials.

[0004] A naturally hard aluminum alloy, which is used as a semifinished material for structures (see the patent RU No. 2085607, IPC class C22 C 21/06), also belongs to the related art as a prototype having the following chemical composition (% by weight): magnesium 3.9-4.9 titanium 0.01-0.1  beryllium 0.0001-0.005  zirconium 0.05-0.15 scandium 0.20-0.50 cerium 0.001-0.004 aluminum balance

[0005] This known alloy does not have sufficient static and dynamic strength, while having high processibility during the manufacturing process, high corrosion resistance, good weldability, and a high readiness for operation under low-temperature conditions.

[0006] The subject matter of the present invention is a new, naturally hard aluminum alloy for semifinished materials which, in addition to magnesium, titanium, beryllium, zirconium, scandium, and cerium, is also made of manganese, copper, zinc, and an element group containing iron and silicon, in the following composition of the components (weight %), the ratio of iron to silicon being in the range of 1 to 5: magnesium 5.0-5.6 titanium 0.01-0.05 beryllium 0.0001-0.005  zirconium 0.05-0.15 scandium 0.18-0.30 cerium 0.001-0.004 manganese 0.05-0.18 copper 0.05-0.15 zinc 0.05-0.15 element group including 0.04-0.24 iron and silicon aluminum balance

[0007] The alloy of the present invention is distinguished from the conventional one by its addition of manganese, copper, zinc, and an element group containing iron and silicon, the components having the following proportions (weights), and the ratio of iron to silicon having to be between 1 and 5: magnesium 5.0-5.6 titanium 0.01-0.05 beryllium 0.0001-0.005  zirconium 0.05-0.15 scandium 0.18-0.30 cerium 0.001-0.004 manganese 0.05-0.18 copper 0.05-0.15 zinc 0.05-0.15 element group including 0.04-0.24 iron and silicon aluminum balance

[0008] The technical effect consists in the improvement of the static and dynamic physical properties of the alloy, which means that the service life, operational reliability, and weight value of the structures subjected to static and dynamic loads improve, in particular those of the structures of various aircraft and spacecraft, including craft that burn cryogenic fuel.

[0009] Due to the present invention's proportions between the chemical levels and the chemical constituents, the alloy has a rather ductile matrix, which is made up of a mixed crystal of dissolved magnesium, manganese, copper, and zinc in aluminum.

[0010] The particularly high readiness of the alloy for operation under cyclical dynamic loads is due to the high ductility of the matrix. Secondary precipitation of finely distributed intermetallic particles, which contain aluminum, scandium, zirconium, titanium, and other transition metals occurring in the alloy, provides for both the high static strength of the alloy and a high resistance to crack propagation during cyclical loading. The setpoint value of the ratio of iron to silicon optimizes the morphology of the primary intermetallic compounds, which result from the solidification, are principally made of aluminum, iron, and silicon, and provide for an improvement in the static strength of the alloy, while its dynamic strength and plasticity are maintained.

EXAMPLE

[0011] Using A85 aluminum, MG90 magnesium, copper MO, zinc TsO, binary key alloys such as aluminum-titanium, aluminum-beryllium, aluminum-zirconium, aluminum-scandium, aluminum-cerium, aluminum-manganese, aluminum-iron, and silumin as an additive, the melt was prepared in an electric oven, on which 165×550 mm flat ingots of the alloy according to the present invention were cast with the aid of semicontinuous casting techniques (Table 1); the ingots having a minimum (composition 1), optimum (composition 2), and maximum (composition 3) proportion of constituents, including proportions of the constituents going beyond the present limitations (compositions 4 and 5), as well as the conventional alloy (composition 6) (see Table 1).

[0012] If the alloy is prepared under metallurgical production conditions, then scrap metal made of aluminum-magnesium alloys may be used as an additive.

[0013] The ingots were homogenized and machined to a thickness of 140 mm. They were subsequently hot-rolled to a thickness of 7 mm at a temperature of 400° C. and then cold-rolled to a thickness of 4 mm. The cold-rolled sheets were heat-treated in an electric oven. The heat-treated sheets were used as test material.

[0014] Standard transverse specimens taken out of the sheets were used to determine the static tensile strength (R_(m), R_(p0,2), A) and the dynamic strength:

[0015] number of cycles to failure (N) in determining the short-term strength (LCF), for which specimens having a notch factor of K_(t)=2.5 and a maximum stress σ_(max)=160 MPa are used;

[0016] crack-propagation speed da/dN in a range of the stress intensity factor ΔK=31.2 MPam^(0.5);

[0017] critical stress intensity factor K_(C) in the state of planar stress, the width (B) of the specimen being 160 mm.

[0018] All tests were conducted at room temperature.

[0019] The test results are listed in Table 2.

[0020] Table 2 verifies that the alloy of the present invention has a higher static and dynamic strength than the conventional alloy. This allows one to reduce the weight of the structures made of the alloy according to the present invention by 10 to 15%, in order to reduce operating costs, which is particularly important to the aircraft industry. The high readiness of the alloy according to the present invention to operate under static and dynamic conditions, as well as the fact that the alloy according to the present invention is a naturally hard alloy having a high corrosion resistance and good weldability, allows one to use it for the construction of completely new aircraft and spacecraft, sea-going vessels, land-bound vehicles, and other vehicles whose structural elements are joined by welding. The alloy according to the present invention may be used as base material in welded structures, and as a welding additive for welded connections. TABLE 2 Chemical Composition, Weight % Iron/ Compo- Magne- Tita- Beryl- Zirco- Scan- Manga- Sili- Sili- Alumi- Alloy sition sium nium lium nium dium Cerium nese Copper Zinc Iron con con*) num Alloy 1 5.0 0.01 0.0001 0.05 0.18 0.001 0.05 0.05 0.05 0.02 0.02 1 Ba- of the lance Present 2 5.3 0.03 0.003 0.1 0.24 0.002 0.12 0.1  0.1  0.10 0.03 3.33 Ba- Inven- lance tion 3 5.6 0.05 0.005 0.15 0.30 0.004 0.18 0.15 0.15 0.2  0.04 5 Ba- lance Expan- 4 4.5 0.005 0.00005 0.01 0.12 0.0005 0.02 0.01 0.01 0.01 0.02 0.5 Ba- ded lance Level 5 6.0 0.1 0.01 0.2 0.36 0.008 0.25 0.25 0.25 0.5  0.08 6.25 Ba of the lance Ele- ments Known 6 4.4 0.05 0.003 0.1 0.3 0.002 — — — — — — Ba- Alloy lance

[0021] TABLE 2 Properties of the Heat-Treated Sheets LCF [cycles] da/dN, (K_(t) = 2.5; [mm/cycle] K_(c) R_(m) R_(p0,2) A σ_(max) = 160 (ΔK = 31.2 [MPa {square root}m] Alloy Composition [MPa] [MPa] [%] MPa) MPa {square root}m) (B = 160 mm) Alloy of the 1 390 275 17 150 · 10³ 2.3 · 10⁻³ 62 Present 2 400 280 16 140 · 10³ 2.5 · 10⁻³ 63 Invention 3 410 290 15 140 · 10³ 3.3 · 10⁻³ 62 Expanded 4 370 260 18 130 · 10³ 3.8 · 10⁻³ 62 Level of the 5 420 315 13 110 · 10³ 4.0 · 10⁻³ 60 Elements Known Alloy 6 380 275 15 130 · 10³ 3.8 · 10⁻³ 62 

1. A naturally hard aluminum alloy as a semifinished material for structures, wherein, in addition to magnesium, titanium, beryllium, zirconium, scandium, and cerium, it is also made of manganese, copper, zinc, and an element group containing iron and silicon, in the following composition of the components (weight %), the ratio of iron to silicon being in the range of 1 to 5: magnesium 5.0-5.6 titanium 0.01-0.05 beryllium 0.0001-0.005  zirconium 0.05-0.15 scandium 0.18-0.30 cerium 0.001-0.004 manganese 0.05-0.18 copper 0.05-0.15 zinc 0.05-0.15 element group including 0.04-0.24 iron and silicon aluminum balance 